Directional antenna system



Dec. 17, 1940. K. KOSCHMIEDER 2,225,456

DIRECTIONAL ANTENNA SYSTEM Filed Sept. 50, 1939 Invemar: KurtKoscflm/eder fHtornQV- Patented Dec. 17, 1940 PATENT OFFICE 2,225,456DIRECTIONAL ANTENNA SYSTEM Kurt. Koschmieder, Falkensee, Ost-Havelland,

Germany, assignor to Lorenz Aktiengesellschaft, Berlin-Tempelhof,Germany, a com- Application September 30, 1939, Serial No. 297,245

- In Germany September 30, 1938 3 Claims.

' This invention briefly relates to directional antenna systems, andmore particularly to means for calibrating such systems. 1

Several types of directional antenna systems areknown in the art. One ofthese types, known as Adcock antenna, comprises four individualantennas, each of which is located in a corner of a square. In acondition of equalization or balance, that is, when the feeder linesinterconnecting the individual antennas and the transmitter neither pickup nor radiate electromagnetic energy, the antenna system operates withsuppressed horizontal polarization. A fifth antenna located in thecentre of the square or point of intersection between the diagonalsconnecting oppositely positioned antennas with one another, completesthe antenna system for the purpose of effecting lateral directiondetermination and for more sharply defining the minimum efiect ofradiation action.

It is a necessary requirement in directional antenna systems, from timeto time, to check or calibrate the efiiciency thereof in respect toeventually occurring unbalances and errors in its directional action. Inthe past such calibration has been efiected from an airplane cruisingaround the antenna system or by a movable transmitter brought around thesystem on a vehicle, for example. The first mentioned method ofcalibration is very expensive and necessitates skilled operators sincenot only electrical direction finding measurements but even opticaldeterminations must be accomplished in order to ascertain errorsintroduced in the action of direction finding. The second method iswearisome and considerably restricted by fields and impassable roads inthe vicinity of the antenna system. A suitable and simple instrument foraccomplishing such calibration has not yet been rendered available.

It is an object of this invention to overcome this lack and to provide asimple and relevant device for calibrating and checking directionalantenna systems. I make use of an auxiliary or calibration transmitterwhich is carried on a bracket member rotatably mounted on the centralantenna of the directional antenna system. It is thus possible to movethis transmitter along the circumference of a circle traced in thecentral portion of and having its mid point coincident with the centralantenna of the system. The

I rotatable bracket member and the fixed pivot are provided with a scaleand pointer, respectively, in order to simplify comparison between theauxiliary transmitter and the eiliciency of the antenna system.

The arrangement according to my invention is beneficially applicable tothe above mentioned Adcock antennas in which direction finding errorsmay immediately be ascertained. It is thus possible in the simplestmanner to determine the operating characteristic of the antenna system.

My invention will be fully understood from the following descriptiontaken in conjunction with the accompanying drawing, in which:

Fig. 1 is a plan view of an Adcock antenna system explanatory of theinvention, while Fig. 2 is a partial cross section through anarrangement according to this invention.

With reference to Fig. 1, there is shown a directional antenna systemcomprising four individual antennas Al, A2, A3 and A4 each disposed inone corner of a square. The antennas Al and A3 and the antennas A2 andA4, respectively, are spaced apart at a distance=d. A fifth antenna A5is located in the centre of the square, in the four corners of which theantennas Al to A4 are placed. Now, as taught by this invention anauxiliary transmitter S is provided. This auxiliary transmitter ismovable along the circumference of a circle K of the diameter D in thecentral portion of the antenna system, that is, around the mid-antennaA5. The auxiliary transmitter S is provided with a dipole or Marconiantenna V. In cases when the transmitter is positioned at 0 or attransit time difierence with respect to the antenna system Al and A3 isa maximum value which is constant and equal to D, while under the samecondition the transit time diiierence is zero for the antenna system A2and A4. On moving the transmitter S along the circumference of thecircle K in a direction toward the antenna A2, the distance 2drepresents the transit time of the currents in the antennas A2 and A4,and 2d'=D sin a. The phase is given by the expression:

21r.D. Sin a In cases when the transmitter would be moved outwardlyalong the azimuth, the action of direction finding remains constantsince the phase change is proportionate for both antenna systems. TheFig. 2 embodies a 'suitable design of the calibration or checking deviceaccording to this invention. The central antenna mast A5 carries awooden bracket H which serves as a support 7 for a small sizetransmitter S having a vertical antenna or dipole V. This bracket and apointer a attached thereto is rotatable around the central antenna overa full 360 degrees scale b which gives the geographic orientation of thedirectional antenna system. When it is desirable to check the efficiencyof the antenna system, the transmitter S may be moved from to degrees soas to determine the minimum effect in the goniometer of the directionalsystem; this minimum being precisely defined in the known manner bymeans of the auxiliary or central antenna A5. Since each change incondition occurringin a directional antenna system causes a directionfinding error, the possibility of arbitrarily repeating the test and thefact that such test only requires a very short time is of beneficialadvantage. It is likewise possible to determine polarization errors byinclining the transmitter dipole V relative to its vertical or normalposition. If this dipole is moved into a horizontal position, noreception takes place in the antenna system.

Because of the fact that the calibration or checking transmitter isfixed to the central, poron f e a t n s st m. he e icie cy there withrespect to the surrounding terrain cannot be determined with thisdevice. This, however, is no essential drawback since eventual changesin this respect are insignificant while the slightest mechanicalunbalance of the antenna system per se might give rise to considerableerrors in the direction finding eificiency.

What is claimed is:

1. An arrangement for calibrating directional antenna systems consistingof a number of individual antennas comprising a calibration transmitter,a dipole antenna directly connected to the said transmitter, asupporting bracket therefor pivotally mounted on an axis at a centralposition of the said directional antenna system and movable. along thecircumference of a circle formed by the saidbracket as the radiusthereof.

2. An antenna arrangement according to claim 1 in which the said axis ata central position of the said directional antenna system is an antennamast forming part thereof.

3. An arrangement according to claim 1 in which a scale is provided onthe said axis and a pointer is provided On the said bracket forascertaining the position of the said calibration transmitter relativeto the geographical orientation of thesaid antenna system.

KU CH ED B-

